1. Field of the Invention
The present invention relates to an optical barrel provided in optical apparatuses such as video cameras and digital still cameras and operable to move an optical element such as a lens in an optical axis direction.
2. Description of the Related Art
Some of optical barrels have a bayonet coupling configuration in which, as disclosed in Japanese Patent No. 3559639, guiding protrusion portions provided in an outer circumferential part of a straight guiding barrel as a first barrel member engage with a circumferentially extending groove portion (hereinafter referred to as “a circumferential groove portion”) formed in an inner circumferential surface of a cam barrel as a second barrel member disposed around the straight guiding barrel. Such a bayonet coupling configuration makes the straight guiding barrel and the cam barrel relatively rotatable with each other around an optical axis (that is, in a circumferential direction). A cam follower provided in an optical element (actually in a holding member holding the optical element) engages with a straight groove portion (through groove portion) formed in the straight guiding barrel so as to extend in an optical axis direction and with a cam groove portion formed in the inner circumferential surface of the cam barrel. In this optical barrel, relative rotation of the straight guiding barrel and the cam barrel causes the cam portion having a cam lift to move the cam follower in the optical axis direction with guiding the cam follower in the same direction by the straight groove portion, and thereby the optical element (holding member) is moved in the optical axis direction.
Moreover, Japanese Patent No. 3559639 discloses an overhang portion provided in the straight guiding barrel so as to extend along an outer circumferential surface of the cam barrel in the optical axis direction (that is, so as to overhang the cam barrel). This overhang portion holds a driven part (slider) of a variable resistor to detect a position of the straight guiding barrel (focal length information) from output of the variable resistor.
However, it is necessary for the optical barrel disclosed in Japanese Patent No. 3559639 to avoid interference between the circumferential groove portion and the cam groove portion formed in the same inner circumferential surface of the cam barrel. In order to avoid this interference, it is in general necessary to divide the inner circumferential surface of the cam barrel in the optical axis direction into an area where the circumferential groove portion is formed and an area where the cam groove portion is formed, which increases length of the cam barrel in the optical axis direction and thereby increases size of the optical barrel and size of an optical apparatus provided therewith.
On the other hand, it is possible to reduce the length of the cam barrel by forming the circumferential groove portion so as to be divided in the circumferential direction at an area where the cam groove portion exists. However, in the area where the circumferential groove portion is divided (that is, where no circumferential groove portion is formed), the guiding protrusion portion of the straight guiding barrel does not engage with the circumferential groove portion, which generates backlash between the straight guiding barrel and the cam barrel in the optical axis direction or which inhibits smooth engagement of the guiding protrusion portion with a next circumferential groove portion in the circumferential direction and thereby may cause defective operation.